Spark plug colour opinions

That's what I would have thought too,but last Saturday I was out for a ride and made it about 2 miles up the trail when the engine quit. It lost all compression in the mag cylinder and something doesn't sound quite right when I roll it over. I'm too frustrated with this whole season to even bother tearing it apart right now,so it looks like a mid summer project. I had just put a new piston,rings and cylinder on the centre after a meltdown the week before this happened. Everything was tore down,crank was inspected,sealed back up properly with case sealant,new base gasket and new o rings for the heads. Fresh gas and ready to roll,only to quite after 2 miles.

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Used a Snap on compression guage to do readings yesterday and got 125,100 and 0 from the PTO to the mag. I'm attributing the low centre reading as hopefully just where it was a new piston and the rings hadn't seated yet.

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So sorry to hear that, I've been exactly where you are at the beginning of the season. Mine turned out to be what I assume, a lean condition on my Viper, due to factory settings on the needle position. We have only been out about 150 km this year because of the lack of snow, after doing the top end again and raising the needles, but it was definitely running cooler.

It's tuff to say what your issue was from the plugs until we see the pistons. Lots of people here that could help with the diagnosis.

I know this is probably a stupid question, but was the sled warmed up before it was launched? What kind of piston was used? Wiseco are prone to cold seizure due to the difference in expansion rate to the cylinder.

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Engine has all OEM parts in it,learned that lesson before,and it was plenty warmed up. It was just odd the way things happened,it never seized just sputtered once and quit. I won't be doing much to the engine til this summer,I just lost all my enthusiasm what with the crappy snow conditions and now 2 breakdowns in 2 weeks,and it is the beginning of April so it'll sit in my trailer until.i get the gumption.

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Yeah that sucks. After reading your post about repairs the week prior a couple of things stand out. Those plug pictures must have been earlier in the season cause those plugs look great. sleds typically don't burn a piston in a moments notice with good looking plugs. Did you run out of gas or oil? Because that certainly would do it.
When you do inspect the engine. Go slow. Look at every part as you disassemble. Pay particular attention to the intake side airbox boots, rubber carb boots, reed gaskets. An air leak will lean out engine fast. Check head torque prior to removal and inspect head o rings looking for leak. And inspect exhaust gasket and flange for an air leak.
Captain obvious would say its gunna be fuel delivery..... or an air leak...... Two miles is such a short distance that i believe something was not assembled correct.
---mac---
 
To be fair these are not the plugs I took out of the engine the week before when I had to rebuild it,they're used plugs that were no doubt out of this engine at one time but were sitting in a container under my bench.The engine is completely stock now but I used to run cut heads at one time.With the uncertainty of gas quality at times I found it easier on the piece of mind to have a stock engine vs shaved heads.The biggest reason I posted the plug pics was to show that there didn't appear to be any leaning out of any cylinders,which I am thinking would've shown up on an old plug easier than a new one.As I stated before the engine never seized up but when I roll it over it just doesn't feel or sound right.I'm hoping it may just be something as simple as a broken ring but my luck is never that good.

There's plenty of oil in the tank and it was bled before I ever started the engine,although I failed to pull the cable so the pump was wide open for a minute or so.As to the gas well I did have an issue with the pump picking up gas after I had siphoned the gas out of the tank,not trusting the quality of it after sitting for about 5 weeks with condensation etc.I will have to make sure to pull the pickup out and either replace it or give it a close inspection before filling the tank next winter.
I tried to make sure I took my time when I rebuilt the engine the week before this issue cropped up.I torqued everything to proper specs,used new gaskets for the base and heads,the only ones not new are the crank seals which looked great.I will no doubt get at tearing this engine down in August so I can get a list of what I need to order to get the beast running again.It just bugs me when it looks that there's no outright visible cause for the cylinder to lose all compression.I could make an educated guess if the piston had seized or burnt a hole in it,but I guess I'll have to wait and see.
 
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